The response section shows that an ItemSearch response
contains two optional (minOccurs=0) elements, OperationRequest and Items. Both of these elements are
references (ref=), which means that they are defined
further down in the WSDL.

This definition also contains several references. One is Arguments, which is defined further down in the WSDL. To fully
understand the definition of the parts of a request, you keep digging down
through the layers of refs. You know that you have reached the end of the
definition hierarchy when you no longer have "ref" in the
element's definition. Instead, the element definition will have a
"name," the name of the element, and "type," which specifies
the element's type. The type will be a base type, such as, string, which is
defined in the schema (xs:), as shown.

<xs:element name="RequestId" type="xs:string" minOccurs="0" />

This line defines RequestId to be of type string, which
is defined by the W3C schema.

When you look at a sample response, shown in the following example, you can
see how the definition of RequestId is carried out.

First, you see that the value for RequestId is string.
Secondly, the name of the element is RequestId. Third,
you can see, in the XML hierarchy, how the definition of RequestId is nested inside the OperationRequest element, which is nested inside of ItermSearchResponse. Remember, it was the "ref"
keyword that created the nesting in the WSDL.